While it is known to incorporate phosphorous into a polymer chain as disclosed in U.S. Pat. No. 3,378,523 and in the publication by G. S. Kolesnikov et al found in Vysokomol-soyed.A9; No. 10, pages 2246-2249, 1947, none of these references discloses the use of minor amounts of particular phosphorus-containing materials to be incorporated into the polymer chain to achieve greatly enhanced thermal stability. Due to the use of increased molding temperatures with polycarbonates and the exposure of molded polycarbonate shapes to higher use temperatures, it is increasingly more important to provide polycarbonates having increased stability to thermal degradation or discoloration due to elevated temperatures.
U.S. Pat. No. 3,378,523 discloses using large quantities of phosphorus-containing compounds and specifically in amounts of 0.2 to 0.5 mole of the phosphorus containing per mole of bisphenol-A. By employing amounts of 0.2 or 20 mole percent of the phosphorus compound of the instant invention, a non-commercial product is obtained.
In U.S. Pat. No. 3,634,312, is is known to prepare copolycarbonate phosphite by incorporating phosphorus in the polymer chain in the form of a phosphite. However, in such a polymer, the polymer make-up is a branched polymer having polymer chain building units in three directions or on three reactive points of the phosphite radical. This is specifically shown in the polymer formula of U.S. Pat. No. 3,634,312. Because of this structure, the polymer of U.S. Pat. No. 3,634,312 exhibits non-Newtonian flow characteristics.